This is a great experiment to introduce students to chemical reactions. The results
which come in less than a week are very exciting to observe. Essentially what happens is
that the copper in the penny reacts with the oxygen in the air to form the green colored
copper oxide.

To spark the students' curiosity even more try simply giving them the directions for
the experiment and tell them to record careful observations over the next week. This way,
the students will not know in advance that some change is necessarily going to occur.
After they have completed their observations, then introduce the concept of a chemical
reaction. A chemical reaction is the combination of two reactants to form an entirely new
product. Bonds are broken and new bonds are made. Simply mixing two substances together
does not necessarily cause a chemical reaction. For example, combining different kinds of
vegetables to make a salad is not a chemical reaction; it is just a mixture of vegetables.
The properties of the individual vegetables do not change. Furthermore no bonds are made
or broken. Examples of chemical reactions and mixtures are given in the
"Assessments" section.

Objectives:

to understand the difference between chemical reactions and mixtures

to understand the difference between a reactant and a product

to explain the effects of acid rain on statues and other objects in our environment

Vocabulary:

chemical

reaction

mixture

reactant

product

Materials:

for each group of students:

(4) copper pennies (before the year 1981 works the best)

(4) small beakers or clear paper cups

approximately 1 tsp. of salt (can either measure or just "eyeball" it) (The
salt just makes the reaction go more quickly.)

enough vinegar to slightly cover the penny sitting in the beaker or cup (The vinegar is
also used make the reaction go more quickly.)

enough water to slightly cover the penny sitting in the beaker or cup

paper and pencil to record observations

tape and marker to label the beakers

spoon (optional)

Procedure:

Place a penny in each beaker.

Sprinkle 1/2 tsp. of salt over the pennies in two of the beakers.

Pour in vinegar to cover one of the pennies with the salt and one of the pennies without
salt.

Label these two beakers with the date and contents (e.g. "2/12/98 -- vinegar and
salt" or "2/12/98 -- vinegar").

Pour in water to cover the other two pennies (one with salt and one without). Label each
of these beakers with the date and appropriate contents.

Record how each beaker looks (i.e. -- the penny and the liquid).

Continue recording observations of each beaker every day for the next week.

Assessments:

Have the students discuss their observations in their groups (i.e. -- which pennies
turned green, which ones turned green first, etc. . . ) F.Y.I. -- they would all turn
green eventually; however, vinegar and salt makes the reaction occur even
quicker.

Give the students examples of chemical reactions and simple mixtures and see if they
can distinguish between the two. Have them discuss their answers in small groups then as a
class to see where their lack of understanding (if any) is coming from. For example:

four irons atoms and three oxygen molecules yields two iron oxide molecules

4. Green pennies -- see this experiment

2Cu+O2-->2CuO

two solid copper atoms and one oxygen molecule yields two copper oxide molecules

Extensions:

Try the experiments cited above in the "Assessments" section for other
exciting examples of chemical reactions.

Incidentally, the reason that the Statue of Liberty turned colors from its original
copper to its present day green is due to a somewhat similar reaction. The statue would
naturally have turned that color due to simple exposure to the oxygen in the air. However,
the acid in acid rain speeds up the reaction just as the vinegar (acetic acid) caused the
reaction with the penny to occur in less than a week.

Philadelphia Science Content Standards:

SCIENCE CONTENT STANDARD # 1: NATURE OF SCIENCE

This experiment satisfies Benchmark 3 for grades 5-8: "collect and summarize data
from an experiment and interpret the results in terms of the data."

SCIENCE CONTENT STANDARD #2: PHYSICAL SETTING
This experiment satisfies Benchmark 5 for grades K-4 because it gives students the
opportunity to "observe how materials change over time". In this case, the
students see how copper statues can change over time.

SCIENCE CONTENT STANDARD #5: DESIGNED WORLD

The introduction to the Philadelphia Science Content Standards states that students
should understand "the impact of science and technology on society." If
connections are made to how the reaction of acid with copper occurs in nature (i.e. the
Statue of Liberty), then students will gain an appreciation of how scientific concepts
have relevance in society.

Cross-references:

This experiment could be used in a chemistry unit on chemical reactions. It could also
be tied in with a lesson on weather (acid rain) or social studies (The Statue of Liberty).